Various techniques have been advanced for the fabrication of can bodies and end closures therefor, principal emphasis being placed upon obtaining the highest possible strength with the least amount of material. Representative of prior art methods which have been employed for forming container ends is that disclosed in the U.S. Patent to Fraze No. 3,572,271. As discussed in that patent, significant cost savings can be realized from a reduction in the amount of metal or material required in making the can end.
Similarly, U.S. Patent to Saunders No. 3,998,174 discloses the formation of a steel container starting with a blank in the form of a shallow depth cup having a thickness on the order of 0.008" to 0.011", ironing only the sidewall of the container to elongate and thin it to about 0.0025" to 0.004", then a bottom end wall profile is formed between complementary male and female profile-forming members to result in an outer chime or rib in an inner recessed panel across the major surface area of the bottom. Numerous other patents discuss and propose different approaches to the formation of can ends, such as, U.S. Patent to Heffner No. 3,957,005 and Wolfe No. 3,831,416.
Although different forming operations have been proposed for reducing the wall thickness of an end closure for a container so as to result in a corresponding reduction in amount of material, weight and cost, none to the best of my knowledge takes the approach of roll-forming the end wall from the interior of a container in such a way as to effect thinning of the metal across the end panel by rolling out the can bottom wall beyond the bottom edge or end of the sidewall which permits the utilization of thinner starting blank gauges while increasing the volume of a container as well as increasing the strength along the bottom wall. This approach is desirable also from the standpoint of reducing original can height, minimizing handling of the can body, and permitting a positive advancing force to be applied from one side only of the end wall in such a way as to assure more uniform thinning or drawing of the metal into a substantially uniform thickness.